The invention discloses a device and method for keeping negative pressure in a pump body of a water pump after shutdown of the water pump. The device comprises a water storage tank, a first solenoid valve, a second solenoid valve, a third solenoid valve, a fourth solenoid valve, a high liquid level sensor and a low liquid level sensor. The work states of the solenoid valves are changed according high and low liquid level changes, and therefore the first solenoid valve and the second solenoid valve from the first set and work synchronously, the third solenoid valve and the fourth solenoid valvefrom the second set and work synchronously, and the two sets of solenoid valves lock each other. A water injection opening, an outer exhaust opening and an inner exhaust opening are arranged at the top of the water storage tank, and a water replenishing opening is arranged at the bottom of the water storage tank. The fourth solenoid valve and the third solenoid valve are arranged on the outer exhaust opening and the water injection opening correspondingly. The second solenoid valve is arranged on an inner drainage opening and is connected with an exhaust pipeline of the pump body of the waterpump through a drainage pipeline. The first solenoid valve is arranged on the water replenishing opening and is connected with the pump body of the water pump through a water replenishing pipe. Two closed sub-containers cooperate with each other and operate independently. When the water pump operates, the water storage tank is full of water through external water, it can be kept that the negativepressure in the pump body is not decreased, and immediate starting of the water pump can be achieved.